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\multicolumn{2}{|c|}{\LARGE\bf THE\hspace*{1cm}STAR\hspace*{1cm}FORMATION\hspace*{1cm}NEWSLETTER} \\ [0.3cm]
\multicolumn{2}{|c|}{\large\em An electronic publication dedicated to early stellar evolution and molecular clouds} \\ [0.3cm]
{\hspace*{0.8cm} No. 112 --- 4 February 2002 } & \multicolumn{1}{r|}{Editor: Bo Reipurth (reipurth@ifa.hawaii.edu)\hspace*{0.8cm}} \\ [-0.1cm]
& \\ \hline
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%{\Large\em From the Editor}
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\begin{center}
{\Large\em Abstracts of recently accepted papers}
\end{center}
\vspace*{0.6cm}
%% Between these brackets you write the title of your paper:
{\large\bf{Warm Molecular Layers in Protoplanetary Disks}}
%% Here comes the author(s) of the paper, please indicate within $^...$
%% the number which corresponds to the institute of each author.
{\bf{ Yuri Aikawa$^1$, Gerd-Jan van Zadelhoff$^2$, Ewine F. van Dishoeck$^2$
\ and Eric Herbst$^3$ }}
%% Here you write your institute name(s) and address(es),
%% the number in $^..$ indicates your author number, for example:
$^1$ {Dept. of Earth and Planetary Science, Kobe University, Kobe 657-8501, Japan} \\
$^2$ {Leiden Observatory, P.O. Box 9513, 2300 RA Leiden, The Netherlands} \\
$^3$ {Departments of Physics and Astronomy, The Ohio State University,
Columbus, OH 43210, USA}
%% Here you may write the e-mail address of one or more of the authors
%% who will act as contact person for preprint requests etc, for example:
{E-mail contact: aikawa@kobe-u.ac.jp}
%% IF YOU USE ANY PERSONAL LATEX COMMANDS IN YOUR ABSTRACT,
%% PLEASE INCLUDE THEIR DEFINITIONS HERE!
\def\gtrsim{\mathrel{\hbox{\rlap{\hbox{\lower4pt\hbox{$\sim$}}}\hbox{$>$}}}}
%% Within the following brackets you place your text:
{We have investigated molecular distributions in
protoplanetary disks, adopting a disk model with a temperature
gradient in the vertical direction. The model produces sufficiently
high abundances of gaseous CO and HCO$^+$ to account for line
observations of T Tauri stars using a sticking probability of unity
and without assuming any non-thermal desorption. In regions of
radius $R\gtrsim 10$ AU, with which we are concerned, the temperature
increases with increasing height from the midplane. In a warm
intermediate layer, there are significant amounts of gaseous molecules
owing to thermal desorption and efficient shielding of ultraviolet
radiation by the flared disk. The column densities of HCN, CN, CS, H$_2$CO,
HNC and HCO$^+$ obtained from our model are in good agreement with the
observations of DM Tau, but are smaller than those of LkCa15.
Molecular line profiles from our disk models are calculated using a
2-dimensional non-local-thermal-equilibrium (NLTE) molecular-line
radiative transfer code for a direct comparison with observations.
Deuterated species are included in our chemical model. The molecular
D/H ratios in the model are in reasonable agreement with those
observed in protoplanetary disks.}
% Here you write which journal accepted your paper, for example:
{ Accepted by Astronomy \& Astrophysics }
%% If preprints are available on the WWW you can give the web
%% direction here.
http://nova.planet.sci.kobe-u.ac.jp/$^{\sim}$aikawa/paper\_list.html
\v5
%% Between these brackets you write the title of your paper:
{\large\bf{Characterization of low-mass pre-main sequence stars
in the Southern Cross}}
%% Here comes the author(s) of the paper, please indicate within $^...$
%% the number which corresponds to the institute of each author.
{\bf{ J.M. Alcal\'a$^1$, E. Covino$^1$, C. Melo$^2$ \ and M.F. Sterzik$^3$ }}
%% Here you write your institute name(s) and address(es),
%% the number in $^..$ indicates your author number, for example:
$^1$ {Osservatorio Astronomico di Capodimonte, 16, I-80131 Napoli, Italy} \\
$^2$ {Observatoire de Gen\`eve, Ch. des Maillettes 51, CH-1290 Sauverny,
Switzerland} \\
$^3$ {European Southern Observatory, Casilla 19001, Santiago 19, Chile}
%% Here you may write the e-mail address of one or more
%% of the authors who will act as contact person for
%% preprint requests etc., for example:
{E-mail contact: jmae@na.astro.it}
%% IF YOU USE ANY PERSONAL LATEX COMMANDS IN YOUR ABSTRACT,
%% PLEASE INCLUDE THEIR DEFINITIONS HERE!
%% Within the following brackets you place your text:
{We report high-resolution spectroscopic observations, as well as
high-resolution near infrared (IR) imaging of six stars previously
identified in a ROSAT pointed observation in the direction of the
B-type star $\beta$~Cru, and classified as low-mass pre-main sequence
(PMS) stars. Four of the stars are confirmed to be low-mass PMS stars,
associated with the Lower Centaurus-Crux group, while the other two
are unrelated to the Sco-Cen association. The confirmed PMS stars are
most likely in their post-T~Tauri evolutionary phase. Although future
deep X-ray observations with high-resolution imagers might detect more
new PMS stars, the possibility that the Crux PMS stars are part of a
small aggregate, with $\beta$~Crux itself approximately at the center,
is rather unlikely, given the high velocity dispersion and the low
spatial density of the confirmed PMS stars. Instead, these stars may
be part of a moving group in a more dispersed and numerous population
of low-mass PMS stars, distributed in the Lower Centaurus-Crux
subgroup. New PMS binaries and multiple systems were also discovered
among the stars in the sample namely, a close visual pair and a
hierarchical triple system in which one of the components is a
double-lined spectroscopic binary (SB2). The detailed orbital
solution is reported for the inner short-period (P$_{orb}$=58.3 days)
SB2. A preliminary orbital solution for the hierarchical triple
system yields a systemic orbital period of about 4.6 years, which
makes this object a very suitable target for follow-up observations
with the Very-Large Telescope Interferometer (VLTI) in the coming
years.}
% Here you write which journal accepted your paper, for example:
{ Accepted by Astron. \& Astrophys. }
%% If preprints are available on the WWW you can give the web
%% direction here.
\v5
%% Between these brackets you write the title of your paper:
{\large\bf{Variability of Southern T Tauri Stars II: The Spectral Variability
of the Classical T Tauri Star TW Hya}}
%% Here comes the author(s) of the paper, please indicate within $^...$
%% the number which corresponds to the institute of each author.
{\bf{ Silvia H.P. Alencar$^1$ and Celso Batalha$^2$ }}
%% Here you write your institute name(s) and address(es),
%% the number in $^..$ indicates your author number, for example:
$^1$ {Universidade de S\~ao Paulo, IAG, Departamento de Astronomia,
Rua do Mat\~ao, 1226, S\~ao Paulo, 05508-900, Brasil} \\
$^2$ {Observat\'orio Nacional, Departamento de Astrofisica,
Rua General Jos\'e Cristino 77, S\~ao Crist\'ov\~ao, Rio de Janeiro,
20921-400, Brasil}
%% Here you may write the e-mail address of one or more
%% of the authors who will act as contact person for
%% preprint requests etc., for example:
{E-mail contact: alencar@iagusp.usp.br}
%% IF YOU USE ANY PERSONAL LATEX COMMANDS IN YOUR ABSTRACT,
%% PLEASE INCLUDE THEIR DEFINITIONS HERE!
\newcommand{\degr}{\hbox{$^\circ$}}
\newcommand \haln{H$\alpha$}
\newcommand \hbeta{H$\beta$~}
\newcommand \kms{km s$^{-1}$~}
\newcommand \kmsn{km s$^{-1}$}
\newcommand \msun{M$_\odot$}
%% Within the following brackets you place your text:
{We present the analysis of 42 spectra of the Classical T Tauri star TW
Hya observed with the FEROS echelle spectrograph over 2 years. We
determined the rotational and radial velocities of TW Hya, obtaining
$v\sin i = 5 \pm 2$ \kms and $v_{rad}=12.5 \pm 0.5$ \kmsn. The star
exhibits strong emission lines that show substantial variety and
variability in their profile shapes. Emission lines such as \haln, \hbeta
and HeI show both outflow and infall signatures, which change on different
timescales.
The system displays periodic variations in line and veiling intensities,
but the stellar rotation period remains uncertain. We see evidence of a
variation in the mass accretion rate over a 1 year period from the NaD
line profiles that are well fitted by magnetospheric accretion models with
moderate mass accretion rates ($10^{-9}$ up to $10^{-8}$ \msun ${\rm
yr}^{-1}$). The lower values inferred from the models are close to the
average mass accretion rate obtained from the veiling estimates ($\sim
2\times 10^{-9}$ \msun ${\rm yr}^{-1}$), but the veiling results are
consistent with a constant a mass accretion rate within the errors of the
calculations.
The \haln, HeI, NaD and \hbeta emission line equivalent widths
corrected from veiling correlate well with each other and are
correlated with the veiling, indicating the same mechanism should be
powering them and suggesting an origin related to the accretion
process. The wings of the main emission lines are generally
correlated, except when the Balmer lines exhibit properties suggesting
a strong contribution from a wind. The blueward absorption components
of the Balmer lines, most likely from awind, are not correlated with
veiling.
The spectroscopic analysis allows us to infer the inclination of the
stellar rotation axis ($i=18\degr \pm 10\degr$) that matches the current
estimations of the disk orientation ($0\degr < i < 15\degr$). A
magnetospheric dipole axis that is misaligned with the stellar/disk
rotation axis could produce the observed photometric variability and we
tend to favor a low inclination but not a totally face-on geometry for the
system. TW Hya exhibits typical spectral characteristics of many classical
T Tauri stars in Taurus, despite its older age, indicating that active
accretion disks can readily survive up to 10 Myr.
}
% Here you write which journal accepted your paper, for example:
{ Accepted by ApJ (scheduled for the v571 May 20, 2002 issue)}
%% If preprints are available on the WWW you can give the web
%% direction here.
{preprints available at
http://www.iagusp.usp.br/$\sim$alencar/twhya/twhya1.html}
\v5
%% Between these brackets you write the title of your paper:
{\large\bf{Physical vs. Observational Properties of Clouds in Turbulent
Molecular Cloud Models}}
%% Here comes the author(s) of the paper, please indicate within $^...$
%% the number which corresponds to the institute of each author.
{\bf{Javier Ballesteros-Paredes$^1$ and Mordecai-Mark Mac Low$^1$}}
%% Here you write your institute name(s) and address(es),
%% the number in $^..$ indicates your author number, for example:
$^1$ {Department of Astrophysics, American Museum of Natural History, New York, USA}
%% Here you may write the e-mail address of one or more of the authors
{E-mail contact: j.ballesteros@astrosmo.unam.mx}
%% IF YOU USE ANY PERSONAL LATEX COMMANDS IN YOUR ABSTRACT,
%% PLEASE INCLUDE THEIR DEFINITIONS HERE!
%% Within the following brackets you place your text:
{We examine the question of how well the physical properties of clumps
in turbulent molecular clouds can be determined by measurements of
observed clump structures. To do this, we compare simulated
observations of three-dimensional numerical models of isothermal,
magnetized, supersonic turbulence to the actual physical structure of
the models. We begin by determining how changing the parameters of the
turbulence changes the structure of the simulations. Stronger driving
produces greater density fluctuations, and longer wavelength driving
produces larger structures. Magnetic fields have a less pronounced
effect on structure, and one that is not monotonic with field
strength. Aligned structures are seen only with low-density tracers,
and when the intensity of the field is large. Comparing different
regions with the same tracers (or conversely, the same region with
different tracers) can give information about the physical conditions
of the region. In particular, different density tracers can help
determine the size of the density fluctuations and thus the strength
of the driving. Nevertheless, velocity superposition of multiple
physical clumps can fully obscure the physical properties of those
clumps, and short wavelength (compared to the size of the region under
analysis) driving worsens this effect. We then compare Larson's
relationships and mass spectra in physical and observational space for
the same structure dataset. We confirm previous claims that the mean
density-size relationship is an observational artifact due to limited
dynamical range in column density: it is the inevitable consequence
presence of a lower cutoff in column density. The velocity
dispersion-size relationship, on the other hand, is reproduced in both
physical and observed clumps, although with substantial scatter in the
derived slope, consistent with observations. Finally, we compute the
mass spectra for the models and compare them to mass spectra derived
from simulated observations of the models. We show that, when we look
for clumps with high enough resolution, they both converge to the same
shape. This shape appears to be log-normal, however, rather than the
power-law function usually used in the literature.}
% Here you write which journal accepted your paper, for example:
{ Accepted by Astrophys. Journal }
%% If preprints are available on the WWW you can give the web
%% direction here.
Preprint available at {\tt
ftp://ftp.astrosmo.unam.mx/pub/j.ballesteros/Papers}
\v5
%% Between these brackets you write the title of your paper:
{\large\bf{Velocity Structure of the ISM as Seen by the Spectral
Correlation Function}}
%% Here comes the author(s) of the paper, please indicate within $^...$
%% the number which corresponds to the institute of each author.
{\bf{Javier Ballesteros-Paredes$^{1,2,3}$, Enrique
V\'azquez-Semadeni$^2$, and Alyssa A.\ Goodman$^3$}}
%% Here you write your institute name(s) and address(es),
%% the number in $^..$ indicates your author number, for example:
$^1$ {Department of Astrophysics, American Museum of Natural History, New York, USA}\\
$^2${Instituto de Astronom\'\i a, Universidad Nacional Aut\'onoma
de M\'exico, Apdo. Postal 70-264, 04510 M\'exico D.F., M\'{e}xico}\\
$^3${Harvard-Smithsonian Center for Astrophysics. 60 Garden St.
MS-42. 02138 Cambridge Ma., USA}
{E-mail contact: j.ballesteros@astrosmo.unam.mx}
%% IF YOU USE ANY PERSONAL LATEX COMMANDS IN YOUR ABSTRACT,
%% PLEASE INCLUDE THEIR DEFINITIONS HERE!
%% Within the following brackets you place your
{We use the statistical tool known as the ``Spectral Correlation
Function" [SCF] to intercompare simulations and observations of the
atomic interstellar medium. The simulations considered, which mimic
three distinct sets of physical conditions, are each calculated for a
300 pc$^3$ box centered at the Galactic plane. Run ``ISM" is intended
to represent a mixture of cool and warm atomic gas, and includes
self-gravity and magnetic fields in the calculations. Run ``ISM-IT"
is more representative of molecular clouds, where the gas is presumed
isothermal. The third run, ``IT" is for purely isothermal gas, with
zero magnetic field, and no self-gravity. Forcing in the three cases
is accomplished by including simulated effects of stellar heating (for
ISM), stellar winds (ISM-IT), or random compressible fluctuations
(IT).
For each simulation, H I spectral-line maps are simulated, and it is
these maps which are intercompared, both with each other, and with
observations, using the SCF. For runs where the separation of velocty
features is much greater than the ``thermal" width of a line,
density-weighted velocity histograms are decent estimates of H I
spectra. When thermal broadening is large in comparison with
fine-scale turbulent velocity structure, this broadening masks
sub-thermal velocity sub-structure in observed spectra. So, simulated
spectra for runs where thermal broadening is important must be
calculated by convolving density-weighted histograms with gaussians
whose width represents the thermal broadening.
The H I observations we use here for comparison are of the North
Celestial Pole Loop, a region chosen to minimize line-of-sight
confusion on scales $> 100$ pc. {\it None} of the simulations match
the NCP Loop data very well, for a variety of reasons described in the
paper. Most of the reasons for simulation/observation discrepancy are
predictable and understandble, but one is particularly curious: the
most realistic ``simulation" comes from {\it artifically expanding}
the velocity axis of run ISM by a factor of six. Without rescaling,
the high temperature associated with much of the gas in run ISM causes
almost all of the spectra to appear as virtually identical gaussians
whose width is deterimined solely by the temperature--all velocity
structure is smeared out by thermal broadening. However, if the
velocity axis is expanded $\times 6$, the SCF distributions of run ISM
an the NCP Loop match up fairly well. This means that the ratio of
thermal to turbulent pressure in run ISM is much too large in the
simulation as it stands, and that either the temperature is much
($\sim 36$ times) lower, and/or that the turbulent energy in the
simulation is much too small. Run ISM does not include the effects of
supernovae, which means that the turbulent energy (and hence velocity
scale) is likely to be dramatically underestimated.
The paper concludes that the SCF is a useful tool for understanding
and fine-tuning simulations of interstellar gas, and in particular
that a realistic simulation of the atomic ISM needs to include the
effects of energetic stellar winds (e.g. supernovae) before the ratio
of thermal-to-turbulent pressure will give spectra representative of
the observed interstellar medium in our Galaxy.
}
% Here you write which journal accepted your paper, for example:
{ Accepted by Astrophys. Journal. }
%% If preprints are available on the WWW you can give the web
%% direction here.
Preprint available at {\tt
ftp://ftp.astrosmo.unam.mx/pub/j.ballesteros/Papers}
\v5
{\large\bf{
Hubble Space Telescope Observations of Proper Motions \\
in Herbig-Haro Objects 1 and 2
}}
{\bf{ John Bally$^1$, Steve Heathcote$^2$, Bo Reipurth$^3$, Jon Morse$^1$, Patrick
Hartigan$^4$, \& Richard Schwartz$^5$ }}
$^1$ CASA, University of Colorado, Boulder, CO 80309, USA\\
$^2$ Cerro Tololo Interamerican Observatory, Casilla 603, La Serena, Chile\\
$^3$ IfA, University of Hawaii, 2680 Woodlawn Drive, Honolulu, HI 96822, USA\\
$^4$ Dept. of Space Physics and Astronomy, Rice University, 6100 S. Main, Houston, TX 77005-1892, USA\\
$^5$ Dept. of Physics and Astronomy, University of Missouri, 8001 Natural Bridge Rd., St. Louis, MO 63121, USA
{E-mail contact: bally@casa.colorado.edu}
Hubble Space Telescope observations obtained in 1994 and 1997 are used
to measure proper motions in the HH 1/2 protostellar outflow in
Orion. Since the HH 1/2 system lies within 10$^o$ of the plane of the
sky, proper motions provide accurate measures of true space
velocities. Comparison of the 1994 and 1997 images reveal a variety of
changes such as the emergence of new knots from the driving source
embedded in the HH 1/2 cloud core and the fading or brightening of
some features. However, such brightness changes affect a small
fraction ($$}}}}
%% Within the following brackets you place your text:
{ We analyse the non-linear propagation and dissipation of
axisymmetric waves in accretion discs using the ZEUS-2D
hydrodynamics code. The waves are numerically resolved in the
vertical and radial directions. Both vertically isothermal and
thermally stratified accretion discs are considered. The waves are
generated by means of resonant forcing and several forms of forcing
are considered. Compressional motions are taken to be locally
adiabatic ($\gamma = 5/3$). Prior to non-linear dissipation, the
numerical results are in excellent agreement with the linear theory
of wave channelling in predicting the types of modes that are
excited, the energy flux by carried by each mode, and the vertical
wave energy distribution as a function of radius. In all cases,
waves are excited that propagate on both sides of the resonance
(inwards and outwards). For vertically isothermal discs, non-linear
dissipation occurs primarily through shocks that result from the
classical steepening of acoustic waves. For discs that are
substantially thermally stratified, wave channelling is the primary
mechanism for shock generation. Wave channelling boosts the Mach
number of the wave by vertically confining the wave to a small cool
region at the base of the disc atmosphere. In general, outwardly
propagating waves with Mach numbers near resonance ${\cal M}_{\rm r}
\ga0.01$ undergo shocks within a distance of order the resonance
radius.
}
% Here you write which journal accepted your paper, for example:
{ Accepted by MNRAS}
%% If preprints are available on the WWW you can give the web
%% direction here.
http://www.astro.ex.ac.uk/people/mbate
\v5
%% Between these brackets you write the title of your paper:
{\large\bf{The Environment and Nature of the Class I Protostar Elias~29:\\
Molecular Gas Observations and the Location of Ices}}
%% Here comes the author(s) of the paper, please indicate within $^...$
{\bf{A.C.A. Boogert$^1$, M.R. Hogerheijde$^2$,
C. Ceccarelli$^3$, A.G.G.M. Tielens$^4$,
E.F. van Dishoeck$^5$, G.A. Blake$^6$,
W.B. Latter$^7$, and F. Motte$^1$ }}
%% Here you write your institute name(s) and address(es),
%% the number in $^..$ indicates your author number, for example:
$^1$ {California Institute of Technology, Downs Laboratory of Physics 320-47,
Pasadena, CA 91125, USA} \\
$^2$ {RAL, Univ. of California at Berkeley, Astronomy
Department, 601 Campbell Hall \# 3411, Berkeley, CA 94720, USA} \\
$^3$ {Observatoire de Bordeaux, B.P. 89, 33270 Floirac, France} \\
$^4$ {Kapteyn Astronomical Institute, P.O. Box 800, 9700 AV
Groningen, the Netherlands} \\
$^5$ {Leiden Observatory, P. O. Box 9513, 2300 RA Leiden, the Netherlands} \\
$^6$ {California Institute of Technology, Division of Geological and
Planetary Sciences 150-21, Pasadena, CA 91125, USA} \\
$^7$ {California Institute of Technology, SIRTF Science
Center, IPAC, Pasadena, CA 91125, USA}
%% Here you may write the e-mail address of one or more of the authors
{E-mail contact: acab@astro.caltech.edu}
%% IF YOU USE ANY PERSONAL LATEX COMMANDS IN YOUR ABSTRACT,
%% PLEASE INCLUDE THEIR DEFINITIONS HERE!
%% Within the following brackets you place your text:
{A (sub-)millimeter line and continuum study of the class I protostar
Elias 29 in the $\rho$ Ophiuchi molecular cloud is presented, whose
goals are to understand the nature of this source, and to locate the
ices that are abundantly present along this line of sight. Within
15--60$''$ beams, several different components contribute to the
line emission. Two different foreground clouds are detected, an
envelope/disk system and a dense ridge of HCO$^+$--rich material. The
latter two components are spatially separated in millimeter
interferometer maps. We analyze the envelope/disk system by using
inside-out collapse and flared disk models. The disk is in a
relatively face-on orientation ($\rm < 60^o$), which explains many
of the remarkable observational features of Elias 29, such as its
flat SED, its brightness in the near infrared, the extended components found in speckle interferometry observations, and its
high velocity molecular outflow. It cannot account for the ices seen
along the line of sight, however. A small fraction of the ices is
present in a (remnant) envelope of mass 0.12--0.33 $M_{\odot}$, but
most of the ices ($\sim$70\%) are present in cool ($T =
30.3$ erg s$^{-1}$ and $ = -3.9$. The X-ray emission
is strongly variable within our exposures in nearly all solar analogs;
about 30 flares with $29.0 < \log L_x(peak) < 31.5$ erg s$^{-1}$ on
timescales from $0.5$ to $>12$ hours are seen during the Chandra
observations. Analogs of the $\leq 1$ My old pre-main sequence Sun
exhibited X-ray flares that are $10^{1.5}$ times more powerful and
$10^{2.5}$ times more frequent than the most powerful flares seen on
the contemporary Sun.
Radio observations indicate that acceleration of particles to relativistic
energies is efficient in young stellar flares. Extrapolating the solar
relationship between X-ray luminosity and proton fluence, we infer that
the young Sun exhibited a $10^5$-fold enhancement in energetic protons
compared to contemporary levels. Unless the flare geometries are
unfavorable, this inferred proton flux on the disk is sufficient to
produce the observed meteoritic abundances of several important
short-lived radioactive isotopes. Our study thus strengthens the
astronomical foundation for local proton spallation models of isotopic
anomalies in carbonaceous chondritic meteorites. The radiation,
particles and shocks produced by the magnetic reconnection flares seen
with $Chandra$ may also have flash melted meteoritic chondrules and
produced excess $^{21}$Ne seen in meteoritic grains.
}
% Here you write which journal accepted your paper, for example:
{ Accepted by Astrophys. J. }
%% If preprints are available on the WWW you can give the web
%% direction here.
Available by anon ftp at: ftp://ftp.astro.psu.edu/pub/edf/ONC\_solar.pdf
\v5
%% Between these brackets you write the title of your paper:
{\large\bf{Far--infrared spectroscopy across the asymmetric bipolar outflows
from Cepheus\,A and L\,1448}}
%% Here comes the author(s) of the paper, please indicate within $^...$
%% the number which corresponds to the institute of each author.
{\bf{D. Froebrich$^1$, M.D. Smith$^2$ \ and J. Eisl\"offel$^1$ }}
%% Here you write your institute name(s) and address(es),
%% the number in $^..$ indicates your author number, for example:
$^1$ {Th\"uringer Landessternwarte Tautenburg, Sternwarte 5, D-07778
Tautenburg, Germany} \\
$^2$ {Armagh Observatory, College Hill, Armagh BT61 9DG, Northern Ireland}
%% Here you may write the e-mail address of one or more
%% of the authors who will act as contact person for
%% preprint requests etc., for example:
{E-mail contact: frobrich@tls-tautenburg.de}
%% IF YOU USE ANY PERSONAL LATEX COMMANDS IN YOUR ABSTRACT,
%% PLEASE INCLUDE THEIR DEFINITIONS HERE!
%% Within the following brackets you place your text:
{Bipolar outflows are driven from protostars within molecular cores. They drive
into molecular clouds, generating shock waves whose molecular emission lines
have been observed in the infrared with ISO. We present spectroscopic data for
seven locations within two asymmetric outflows, Cepheus\,A and L\,1448, in
order to test the shock physics and shock dynamics. Here, we simultaneously
interpret the CO and H$_2$ data sets which are generated by shocked gas,
radiating at temperatures from 300 to 2000\,K. We find that large-scale spatial
variations in the excitation are absent across both outflows and that the
excitation is low everywhere. \\ Planar shock models are inconsistent with the
data sets. Models with configurations or ensembles of shocks, in the form of
bow shocks or supersonic turbulence, are consistent. This solves the previously
reported problem that the CO abundances were anomalously high. Cool gas is
dominant, from which we infer bow shocks with flanks more extended than for
paraboloids. As a consequence, the atomic oxygen abundances must be quite low.
J-type bow models require implausibly long wings. C-type physics is thus
favoured. \\ The density and the ratio of molecules to atoms are constrained by
the CO/H$_2$ flux levels as well as the H$_2$ vibrational level distributions.
Other C-shock parameters, such as the magnetic field strength, ion fraction
and speed, are not tightly constrained. The total shock powers are derived and
are comparable to the mechanical outflow luminosities for both outflows,
consistent with the outflows being momentum-driven. }
% Here you write which journal accepted your paper, for example:
{ Accepted by A\&A }
%% If preprints are available on the WWW you can give the web
%% direction here.
Preprints are available at http://www.tls-tautenburg.de/research/research.html
\v5
%% Between these brackets you write the title of your paper:
{\large\bf{The FUV spectrum of TW Hya. I. Observations of H$_2$
Fluorescence}}
%% Here comes the author(s) of the paper, please indicate within $^...$
%% the number which corresponds to the institute of each author.
{\bf{Gregory J. Herczeg$^1$, Jeffrey L. Linsky$^1$, Jeff A. Valenti$^2$,
Chris
M. Johns-Krull$^3$, and Brian E. Wood$^1$ }}
%% Here you write your institute name(s) and address(es),
%% the number in $^..$ indicates your author number, for example:
$^1$ {JILA, University of Colorado, Boulder, CO 80309, USA}\\
$^2$ {Space Telescope Science Institute, Baltimore, MD 21218, USA}\\
$^3$ {
Dept. of Space Physics and Astronomy, Rice University, 6100 S. Main, Houston, TX 77005-1892, USA
}
%% Here you may write the e-mail address of one or more of the authors
%% who will act as contact person for preprint requests etc, for example:
{E-mail contact: gregoryh@casa.colorado.edu}
%% IF YOU USE ANY PERSONAL LATEX COMMANDS IN YOUR ABSTRACT,
%% PLEASE INCLUDE THEIR DEFINITIONS HERE!
%% Within the following brackets you place your text:
{We observed the classical T Tauri star TW Hya with \textit{HST}/STIS
using the E140M grating, from 1150--1700 \AA,
with the E230M grating, from 2200--2900 \AA, and with FUSE from
900--1180 \AA. Emission in 143 Lyman-band H$_2$ lines
representing 19 progressions dominates the spectral region from
1250--1650 \AA.
The total H$_2$ emission line flux is $1.94 \times 10^{-12}$ erg cm$^{-2}$
s$^{-1}$, which corresponds to $1.90\times10^{-4}$ $L_\odot$ at TW Hya's
distance of 56 pc. A
broad stellar Ly$\alpha$ line photoexcites the H$_2$ from excited
rovibrational levels of the ground electronic state to
excited electronic states.
The C II 1335 \AA\ doublet, C III 1175 \AA\ multiplet, and
C IV 1550 \AA\ doublet also electronically excite H$_2$.
The
velocity shift of the H$_2$ lines is consistent with the photospheric
radial velocity of TW Hya, and the emission is not spatially extended
beyond the $0.05^{\prime\prime}$ resolution of \textit{HST}.
The H$_2$ lines have an intrinsic FWHM of $11.91\pm0.16$ km s$^{-1}$.
One H$_2$ line is
significantly weaker than predicted by this model because of C II
wind absorption. We also do not observe any H$_2$ absorption against the
stellar Ly$\alpha$ profile. From these results, we conclude that the
H$_2$
emission is
more consistent with an origin in a disk rather than in an outflow or
circumstellar shell.
We also analyze the hot accretion-region lines
(e.g., C IV, Si IV, O VI) of TW Hya, which
are formed at the accretion shock, and discuss some reasons why Si lines
appear
significantly weaker than other TR region lines.}
% Here you write which journal accepted your paper, for example:
{ Accepted by ApJ}
%% If preprints are available on the WWW you can give the web
%% direction here.
http://xxx.lanl.gov/abs/astro-ph/0201319
\v5
%% Between these brackets you write the title of your paper:
{\large\bf{Discovery of Reflection Nebulosity Around Five Vega-like Stars}}
%% Here comes the author(s) of the paper, please indicate within $^...$
%% the number which corresponds to the institute of each author.
{\bf{Paul Kalas$^{1,2}$, James R. Graham$^{1,2}$, Steven V.W. Beckwith$^3$,
David C. Jewitt$^4$ \ and James P. Lloyd$^{1,2}$ }}
%% Here you write your institute name(s) and address(es),
%% the number in $^..$ indicates your author number, for example:
$^1$ {Astronomy Department, University of California, Berkeley, CA 94720, USA} \\
$^2$ {NSF Center for Adaptive Optics, University of California,
Santa Cruz, CA 95064, USA} \\
$^3$ {Space Telescope Science Institute, Baltimore, MD 21218, USA
} \\
$^4$ {Institute for Astronomy, University of Hawaii, Honolulu, HI 96822, USA}
%% Here you may write the e-mail address of one or more
%% of the authors who will act as contact person for
%% preprint requests etc., for example:
{E-mail contact: kalas@astro.berkeley.edu}
%% IF YOU USE ANY PERSONAL LATEX COMMANDS IN YOUR ABSTRACT,
%% PLEASE INCLUDE THEIR DEFINITIONS HERE!
%% Within the following brackets you place your text:
{
Coronagraphic optical observations of six Vega-like stars reveal
reflection nebulosities, five of which were previously unknown.
The
nebulosities illuminated by HD 4881, HD 23362, HD 23680,
HD 26676, and HD 49662 resemble
that of the Pleiades, indicating an interstellar origin for dust
grains.
The reflection nebulosity
around HD 123160 has a double-arm morphology, but no disk-like
feature is seen as close as 2.5 arcseconds from the star
in K-band adaptive optics data. We demonstrate that uniform density dust clouds
surrounding HD 23362, HD 23680 and HD 123160 can account for
the observed 12$-$100 $\mu$m spectral energy distributions.
For HD 4881, HD 26676, and HD 49662 an additional emission
source, such as from a circumstellar disk or non-equilibrium
grain heating, is required to fit the 12$-$25 $\mu$m data.
These results indicate that in some cases, particularly
for Vega-like stars located beyond the Local Bubble ($>$100 pc),
the dust responsible for excess thermal emission
may originate from the interstellar medium rather than from
a planetary debris system.
}
%% Here you write which journal accepted your paper, for example:
{Accepted by The Astrophysical Journal (March, 2002)}
%% If preprints are available on the WWW you can give the web
%% direction here.
\v5
%% Between these brackets you write the title of your paper:
{\large\bf{The Initial Mass Function of Stars: Evidence for
Uniformity in Variable Systems
}}
%% Here comes the author(s) of the paper, please indicate within $^...$
%% the number which corresponds to the institute of each author.
{\bf{Pavel Kroupa}}
%% Here you write your institute name(s) and address(es),
%% the number in $^..$ indicates your author number, for example:
{Institute of Theoretical Physics and Astrophysics, University of
Kiel, D-24098 Kiel, Germany}
%% Here you may write the e-mail address of one or more
%% of the authors who will act as contact person for
%% preprint requests etc., for example:
{E-mail contact: pavel@astrophysik.uni-kiel.de}
%% IF YOU USE ANY PERSONAL LATEX COMMANDS IN YOUR ABSTRACT,
%% PLEASE INCLUDE THEIR DEFINITIONS HERE!
%% Within the following brackets you place your text:
{The distribution of stellar masses that form in one star-formation
event in a given volume of space is called the initial mass function
(IMF). The IMF has been estimated from low-mass brown dwarfs to very
massive stars. Combining IMF estimates for different populations in
which the stars can be observed individually unveils an extraordinary
uniformity of the IMF. This general insight appears to hold for
populations including present-day star formation in small molecular
clouds, rich and dense massive star-clusters forming in giant clouds,
through to ancient and metal-poor exotic stellar populations that may
be dominated by dark matter. This apparent universality of the IMF is
a challenge for star formation theory because elementary
considerations suggest that the IMF ought to systematically vary with
star-forming conditions. }
% Here you write which journal accepted your paper, for example:
{ Accepted by Science }
%% If preprints are available on the WWW you can give the web
%% direction here.
http://xxx.uni-augsburg.de/abs/astro-ph/0201098
\v5
%% Between these brackets you write the title of your paper:
{\large\bf{Thickening of galactic disks through clustered star formation
}}
%% Here comes the author(s) of the paper, please indicate within $^...$
%% the number which corresponds to the institute of each author.
{\bf{ Pavel Kroupa}}
%% Here you write your institute name(s) and address(es),
%% the number in $^..$ indicates your author number, for example:
{Institute of Theoretical Physics and Astrophysics, University of
Kiel, D-24098 Kiel, Germany}
%% Here you may write the e-mail address of one or more
%% of the authors who will act as contact person for
%% preprint requests etc., for example:
{E-mail contact: pavel@astrophysik.uni-kiel.de}
%% IF YOU USE ANY PERSONAL LATEX COMMANDS IN YOUR ABSTRACT,
%% PLEASE INCLUDE THEIR DEFINITIONS HERE!
%% Within the following brackets you place your text:
{The building blocks of galaxies are star clusters. These form with
low-star formation efficiencies and, consequently, loose a large part
of their stars that expand outwards once the residual gas is expelled
by the action of the massive stars. Massive star clusters may thus add
kinematically hot components to galactic field populations. This
kinematical imprint on the stellar distribution function is estimated
here by calculating the velocity distribution function for ensembles
of star-clusters distributed as power-law or log-normal initial
cluster mass functions (ICMFs). The resulting stellar velocity
distribution function is non-Gaussian and may be interpreted as being
composed of multiple kinematical sub-populations.
The velocity-dispersion of solar-neighbourhood stars increases more
rapidly with stellar age than theoretical calculations of orbital
diffusion predict. Interpreting this difference to arise from star
formation characterised by larger cluster masses, rather than as yet
unknown stellar-dynamical heating mechanisms, suggests that the star
formation rate in the MW disk has been quietening down, or at least
shifting towards less-massive star-forming units. Thin-disk stars
with ages 3--7~Gyr may have formed from an ICMF extending to very rich
Galactic clusters. Stars appear to be forming preferentially in
modest embedded clusters during the past~3~Gyr.
Applying this approach to the ancient thick disk of the Milky Way, it
follows that its large velocity dispersion may have been produced
through a high star formation rate and thus an ICMF extending to
massive embedded clusters ($\approx10^{5-6}\,M_\odot$), even under the
extreme assumption that early star formation occurred in a thin
gas-rich disk. This enhanced star-formation episode in an early thin
Galactic disk could have been triggered by passing satellite galaxies,
but direct satellite infall into the disk may not be required for disk
heating.
}
% Here you write which journal accepted your paper, for example:
{ Accepted by MNRAS }
%% If preprints are available on the WWW you can give the web
%% direction here.
http://xxx.uni-augsburg.de/abs/astro-ph/0111175
\vspace{0.3cm}
%% Between these brackets you write the title of your paper:
{\large\bf{Ongoing Star Formation Activity in the L\,1340 Dark Cloud}}
%% Here comes the author(s) of the paper, please indicate within $^...$
%% the number which corresponds to the institute of each author.
{\bf{ M.~S.\ Nanda Kumar$^1$, B.~G.\ Anandarao$^1$ \ and Ka Chun
Yu$^3$ }}
%% Here you write your institute name(s) and address(es),
%% the number in $^..$ indicates your author number, for example:
$^1$ {Physical Research Laboratory, Navrangapura,
Ahmedabad 380009, India} \\
$^2$ {Center for Astrophysics and Space Astronomy,
University of Colorado, Boulder, CO 80303, USA}
%% Here you may write the e-mail address of one or more of the authors
%% who will act as contact person for preprint requests etc, for example:
{E-mail contact: nanda@oan.es}
%% IF YOU USE ANY PERSONAL LATEX COMMANDS IN YOUR ABSTRACT,
%% PLEASE INCLUDE THEIR DEFINITIONS HERE!
%% Within the following brackets you place your text:
{We present a study of the L\,1340 molecular cloud
that is known to be actively forming low and intermediate mass stars
in three independent cores. We present optical and NIR images of the
central regions of the three cores of this cloud, better known as
RNO\,7, RNO\,8 and RNO\,9. We show that RNO\,7 is a Herbig Be
cluster. We have discovered three Herbig-Haro flows in core~A (south
western part) of the cloud that are named HH\,487, HH\,488 and
HH\,489. HH\,487 is a spectacular set of bowshocks that appear to be
driven by IRAS~02224+7227. HH\,488a is a $\sim$ 3.4$'$ long
flow possibly overlaping with a second flow(HH\,488b)in the line of
sight. HH\,489 is a flow extending to $\sim$ 1$'$ on either
side of the driving source IRAS~02249+7230. Most of these HH objects
are found to be high excitation objects.}
% Here you write which journal accepted your paper, for example:
{ Accepted by Astron. J. }
%% If preprints are available on the WWW you can give the web
%% direction here.
\vspace{0.3cm}
%% Between these brackets you write the title of your paper:
{\large\bf{The ISO-LWS map of the Serpens cloud core. II. The line
spectra}}
%% Here comes the author(s) of the paper, please indicate within $^...$
%% the number which corresponds to the institute of each author.
{\bf{ Bengt Larsson$^1$, Ren\'e Liseau$^1$ \ and Alexander B.
Men'shchikov$^2$ }}
%% Here you write your institute name(s) and address(es),
%% the number in $^..$ indicates your author number, for example:
$^1$ {Stockholm Observatory, SCFAB, Roslagstullsbacken 21, SE-106 91
Stockholm, Sweden} \\
$^2$ {Max-Planck-Institut f\"ur Radioastronomie, Auf dem H\"ugel, Bonn,
Germany}
%% Here you may write the e-mail address of one or more of the authors
%% who will act as contact person for preprint requests etc, for
{E-mail contact: bem@astro.su.se}
%% IF YOU USE ANY PERSONAL LATEX COMMANDS IN YOUR ABSTRACT,
%% PLEASE INCLUDE THEIR DEFINITIONS HERE!
\newcommand{\molh}{H$_{2}$} %H_2, H_2O and H II
\newcommand{\oishort}{[O\,{\sc i}]\,63\,$\mu$m}
\newcommand{\ctwo}{[C\,{\sc ii}]\,157\,$\mu$m} %fine structure lines
\newcommand{\cthree}{[C\,{\sc i}]\,370\,$\mu$m}
\newcommand{\iso}{ISO}
\newcommand{\lws}{LWS}
\newcommand{\cam}{CAM}
\newcommand{\cvf}{CVF}
%\newcommand{\kms}{km\,s$^{-1}$}
\newcommand{\amin}{$^{\prime}$}
\newcommand{\asec}{$^{\prime \prime}$}
\newcommand{\adeg}{$^{\circ}$}
\newcommand{\cmthree}{cm$^{-3}$}
\newcommand{\water}{H$_{2}$O}
\newcommand{\powten}[1]{10$^{#1}$}
%\newcommand{\msun}{$M_{\odot}$}
\newcommand{\scc}{${\rm Serpens \, cloud \, core}$}
\newcommand{\av}{$A_{\rm V}$}
\newcommand{\pdr}{PDR}
%% Within the following brackets you place your text:
{We present spectrophotometric \iso\ imaging with the \lws\ and the
\cam-\cvf\ of the Serpens molecular cloud core. The \lws\ map is
centred on the far infrared and submillimetre sourceFIRS\,1/SMM\,1 and
its size is 8\amin\,$\times$\,8\amin. The fine structure line
emission in \oishort\ and \ctwo\ is extended on the arcminute scale
and can be successfully modelled to originate in a \pdr\ with $G_0 =
15 \pm 10$ and $n$(\molh) in the range of $(10^4 -
10^5)$\,\cmthree. Extended emission might also be observed in the
rotational line emission of \water\ and high-$J$ CO. However, lack of
sufficient angular resolution prevents us from excluding the
possibility that the emssion regions of these lines are point like,
which could be linked to the embedded objects SMM\,9/S\,68 and SMM\,4.
Toward the Class\,0 source SMM\,1, the \lws\ observations reveal, in
addition to fine structure line emission, a rich spectrum of molecular
lines, superposed onto a strong, optically thick dust continuum
(Larsson et al. 2000). The sub-thermally excited and optically thick
CO, \water\ and OH lines are tracing an about \powten{3}\,AU source
with temperatures higher than 300\,K and densities above
\powten{6}\,\cmthree\ ($M=0.01$\,\msun). The molecular abundances,
$X=N({\rm mol})/N$(\molh), are $X=(1,\,0.1,\,0.02,\,\ge 0.025) \times
10^{-4}$ for CO, \water, OH and $^{13}$CO, respectively. Our data are
consistent with an ortho-to-para ratio of 3 for \water. OH appears
highly overabundant, which we tentatively ascribe to an enhanced
(X-ray) ionisation rate in the \scc\ ($\zeta \gg 10^{-18}\,{\rm
s}^{-1}$). We show that geometry is of concern for the correct
interpretation of the data and based on 2D-radiative transfer
modelling of the disk/torus around SMM\,1, which successfully
reproduces the entire observed SED and the observed line profiles of
low-to-mid-$J$ CO isotopomers, we can exclude the disk to be the
source of the \lws-molecular line emission. The same conclusion
applies to models of dynamical collapse (`inside-out' infall). The
6\asec\ pixel resolution of the \cam-\cvf\ permits us to see that the
region of rotational \molh\ emission is offset from SMM\,1 by 30\asec,
at position angle 340\adeg, which is along the known jet flow from the
Class\,0 object. This \molh\ gas is extinguished by \av\,=\,4.5\,mag
and at a temperature of \powten{3}\,K, which suggests that the heating
of the gas is achieved through relatively slow shocks. This is also in
agreement with the deduced low ortho-to-para ratio of \molh-$o/p =1$.
Although we are not able to establish any firm conclusion regarding
the detailed nature of the shock waves, our observations of the
molecular line emission from SMM\,1 are to a limited extent
explainable in terms of an admixture of J-shocks and of C-shocks, the
latter with speeds of about (15--20)\,\kms, whereas dynamical infall
is not directly revealed by our data. }
% Here you write which journal accepted your paper, for example:
{ Accepted by A\&A }
%% If preprints are available on the WWW you can give the web
%% direction here.
\vspace{0.3cm}
%% Between these brackets you write the title of your paper:
{\large \bf{
New determinations of the critical velocities for C-type shock waves in dense
molecular clouds: application to the outflow source in Orion}}
%% Here comes the author(s) of the paper, please indicate within $^...$
%% the number which corresponds to the institute of each author.
{\bf{J. Le Bourlot$^{1}$, G. Pineau des For\^ets$^{2}$,
D. R. Flower$^{3}$, S. Cabrit$^{4}$}}
%% Here you write your institute name(s) and address(es),
%% the number in $^..$ indicates your author number, for example:
$^1$ {Observatoire de Paris, DAEC, F-92195 Meudon Principal Cedex}\\
$^2$ {Institut d'Astrophysique Spatiale, Orsay, France}\\
$^3$ {Physics Department, The University Durham DH1 3LE, UK}\\
$^4$ {Observatoire de Paris, UMR 8540 du CNRS, 61 Avenue de
l'Observatoire, F-75014 Paris}
%% Here you may write the e-mail address of one or more
%% of the authors who will act as contact person for
%% preprint requests etc., for example:
{E-mail contact: jacques.lebourlot@obspm.fr, david.flower@durham.ac.uk}
%% IF YOU USE ANY PERSONAL LATEX COMMANDS IN YOUR ABSTRACT,
%% PLEASE INCLUDE THEIR DEFINITIONS HERE!
\def\H2{H$_2$}
\def\cm{cm$^{-3}$}
\def\kms{km~s$^{-1}$}
%% Within the following brackets you place your text:
{We report calculations of the intensities of rovibrational transitions of
\H2\ emitted from C-type shock waves propagating in molecular
gas. Attention was paid to the thermal balance of the gas and to the rates
of collisional dissociation and ionization of \H2. We found that the
maximum shock speeds which can be attained, prior to the collisional
dissociation of \H2\ (which results in a sonic point in the flow and hence
a J-type shock wave), can be much higher than had previously been
believed. Thus, adopting the ``standard'' scaling of the transverse
magnetic induction with the gas density, B/$\mu$G = $\sqrt{\rm nH/cm^{-3}}$, we
established that the maximum shock speed increased from 20-30 \kms\ at high
pre-shock densities (nH $\ge 10^6$ \cm) to 70-80 \kms\ at low densities (nH
$\le 10^4$ \cm). The critical shock speed, Vcrit, also increases
significantly with the transverse magnetic induction, B, at a given
preshock gas density nH.
By way of an application of these results, we demonstrate that a
two-component model, comprising shock waves with nH = $10^4$ \cm\ and
velocities vs = 60 \kms\ and 40 \kms, reproduces the column densities of
\H2\ observed by ISO-SWS (Rosenthal et al. 2000) up to the highest level
(possibly) detected, v = 0, J = 27, which lies 42~515 K above the ground
state. We find no necessity to invoke mechanisms other than thermal
collisional excitation in the gas phase; but the v = 1 vibrational band
remains less completely thermalized than is indicated by the observations.
Fine structure transitions of atoms and ions were also considered. The
intensity of the [Si I] 68.5 $\mu$m transition, observed by Gry et
al. (1999) using ISO-LWS, is satisfactorily reproduced by the same model
and may also originate in OMC-1, rather than Orion-KL as originally
believed. The transitions of [Fe II] and [S I], observed by Rosenthal et
al. (2000), may also arise in the shock-heated gas.
Predicted level populations of \H2\ for our full grid of C-shock models
(densities of $10^3, 10^4, 10^5, 10^6, 10^7$ \cm\ and shock speeds
ranging from 10 \kms\ to Vcrit) are made
available on the WWW at {\tt http://ccp7.dur.ac.uk/pubs.html}.
}
% Here you write which journal accepted your paper, for example:
{ Accepted by Monthly Notices of the Royal Astronomical Society }
%% If preprints are available on the WWW you can give the web
%% direction here.
{\tt http://ccp7.dur.ac.uk/pubs.html}
\clearpage
%% Between these brackets you write the title of your paper:
{\large\bf{Crossing the Brown Dwarf Desert Using Adaptive Optics:\\A Very
Close L-Dwarf Companion to the Nearby Solar Analog HR~7672}}
%% Here comes the author(s) of the paper, please indicate within $^...$
%% the number which corresponds to the institute of each author.
{\bf{ Michael C. Liu$^1$, Debra A. Fischer$^2$, James R. Graham$^2$, James
P. Lloyd$^2$, Geoff W. Marcy$^2$, R. Paul Butler$^3$}}
%% Here you write your institute name(s) and address(es),
%% the number in $^..$ indicates your author number, for example:
$^1$ {Institute for Astronomy, University of Hawai`i, 2680 Woodlawn
Drive, Honolulu, HI 96822, USA} \\
$^2$ {Department of Astronomy, 601 Campbell Hall, University of
California, Berkeley, CA 94720, USA}\\
$^3$ {Department of Terrestrial Magnetism, Carnegie Institution of
Washington, 5241 Broad Branch Road, NW, Washington DC, 20015-1305, USA}
%% Here you may write the e-mail address of one or more
%% of the authors who will act as contact person for
%% preprint requests etc., for example:
{E-mail contact: mliu@ifa.hawaii.edu}
%% IF YOU USE ANY PERSONAL LATEX COMMANDS IN YOUR ABSTRACT,
%% PLEASE INCLUDE THEIR DEFINITIONS HERE!
\newcommand{\Mjup}{\mbox{$M_{Jup}$}}
\def\farcs{\hbox{$.\!\!^{\prime\prime}$}}
\newcommand{\micron}{\mbox{$\mu{\rm m}$}}
\def\lesssim{\mathrel{\hbox{\rlap{\hbox{%
\lower4pt\hbox{$\sim$}}}\hbox{$$}}}
%% Within the following brackets you place your text:
{Using high resolution near-infrared spectroscopy with the Keck telescope, we
have detected the radial velocity signatures of the cool secondary components
in four optically identified pre$-$main-sequence, single-lined spectroscopic
binaries. All are weak-lined T Tauri stars with well-defined center of mass
velocities. The mass ratio for one young binary, NTTS 160905$-$1859, is
M$_2$/M$_1$ $=$ 0.18$\pm$0.01,
the smallest yet measured dynamically for a pre$-$main-sequence
spectroscopic binary.
These new results demonstrate the power of infrared spectroscopy for the
dynamical identification of cool secondaries. Visible light spectroscopy, to
date, has not revealed any pre$-$main-sequence secondary stars with masses
$